Energy Changes Flashcards
What is an exothermic reaction?
A reaction that releases energy to the surroundings, usually as heat, causing the temperature to rise.
Give an example of an exothermic reaction.
Combustion (e.g., burning wood or fuel), neutralization of an acid and an alkali.
What is an endothermic reaction?
Combustion (e.g., burning wood or fuel), neutralization of an acid and an alkali.
What is an endothermic reaction?
A reaction that absorbs energy from the surroundings, usually as heat, causing the temperature to fall.
Give an example of an endothermic reaction.
The thermal decomposition of calcium carbonate (CaCO₃ → CaO + CO₂).
What is activation energy?
The minimum energy required for a chemical reaction to occur.
How does activation energy affect a reaction?
Reactions require enough energy to break bonds in reactants, so a higher activation energy means the reaction is slower.
How can the activation energy of a reaction be reduced?
By using a catalyst, which provides an alternative reaction pathway with a lower activation energy.
What is an energy profile diagram?
A diagram that shows how the energy of the system changes during a reaction.
In an exothermic reaction, what happens to the energy of the system?
The energy decreases as the products have lower energy than the reactants.
In an endothermic reaction, what happens to the energy of the system?
The energy increases as the products have higher energy than the reactants.
How do you identify whether a reaction is exothermic or endothermic from an energy profile diagram?
If the products have lower energy than the reactants, the reaction is exothermic. If the products have higher energy, the reaction is endothermic.
How do you calculate the energy change of a reaction?
Energy change = Energy of products - Energy of reactants.
What is the formula for the energy released in an exothermic reaction?
Energy released = Bond energies of reactants - Bond energies of products.
In an endothermic reaction, is energy absorbed or released?
Energy is absorbed from the surroundings.
What is bond energy?
The energy required to break a bond in a molecule, or the energy released when a bond is formed.
Why is energy required to break bonds?
Bonds are a form of stored energy, and breaking them requires energy to overcome the attractive forces between atoms.
Why is energy released when bonds are formed?
When new bonds form, energy is released as the atoms become more stable.
How do you calculate the energy change in a reaction using bond energies?
Energy change = Energy required to break bonds - Energy released when bonds are formed.
Why are exothermic reactions useful in everyday life?
They release heat, which is useful in processes such as combustion (e.g., burning fuels to heat homes) or self-heating cans.
Why are endothermic reactions useful in everyday life?
They absorb heat, which is useful for cooling purposes, such as in sports injury packs.
How is energy change involved in batteries?
Batteries involve exothermic reactions that produce a flow of electrons to create electricity.
What happens to energy in a reversible reaction?
The energy change for the forward reaction is equal in size but opposite in sign to the energy change for the reverse reaction.
How can energy changes in reversible reactions be used?
In hydrogenation (adding hydrogen to unsaturated fats), the reverse reaction can absorb energy to break down fats, and the forward reaction releases energy when the fats are made.
How do electrochemical cells use energy changes?
Electrochemical cells use oxidation and reduction reactions to produce electricity, with energy released during the reactions.
What is a fuel cell?
A device that converts the chemical energy of a fuel (e.g., hydrogen) directly into electrical energy through oxidation and reduction reactions.
How does a fuel cell generate energy?
A fuel (like hydrogen) reacts with oxygen, releasing energy in the form of electricity and water as a byproduct.
